No compression when engine is cold

[Krtek]

My boyfriend's XL600R runs fine, but is a bitch to start. Especially when it's been standing still for a week or more there's virtually no compression at all.
If you can get it to run a few strokes, then it starts building up some compression, and once it runs, it runs very well and idles fine too.
If you switch it off at that point, the compression then feels normal / good.

If it's been running, say, a few hours ago, there is very little compression but just about enough to start it with a few kicks. But after a couple of days it's hopeless.

Does this sound familiar to anyone?
Where should we start looking for a solution? Rings, valves, valve seals?

[AIRWOLF]

had similar with an 86 xr250 (rfvc), when parked for a week or two, . little compression, . . once started it would 'tick' like a loose tappet for a minute then go quiet and then normal compression rest of day. . . . i suspected sticking valve, . . . stripped top end, new rings, grind valves in, inspect valve train, all seemed ok. . . . on re-assembly, good compression, started easy, no ticking. . . .
left a few days, . . . low compression, ticking when started obviously missed something . . . . .
so i figured if valve is sticking open, park up with engine on compression ie valves closed, see what happens, . . . . try a few days later, good compression, starts easy, no ticking
obviously something sticking, valve/valve train, . . . but park up on compression , no problem. and ok to this day.
so yes, as you say rings/valves, but the 'extra bits' in the rfvc head can be a pain, so pay attention there.
good luck

[Krtek]

Thanks! We will certainly try this, and see what happens.
The engine on this one doesn't tick, but everything else sounds similar, so the problem might well be similar in nature.

[stretchy]

Exactly the same problem with an XR250 I have, twas the cam chain, stretched it was!

Check the timing marks ALL line up.

Not sure on your bike but flywheel TDC mark needs to coincide with marks on cam sprocket.

And of course as the previos post Check the valve clearence. Improper adjustment will cause the exhaust valve seat to get burnt normally.

If the timing marks dont line up pull the head and poor fuel thru' the in and out ports to see if it leeks............easy.

'Reet.

[Krtek]

Thanks! Valve clearance is fine (we keep an eye on that), but stretched chain sounds interesting.

There's no audible chain slack though, in fact the engine sounds nice and clean.

[stretchy]

Mine sounded fine too just wouldn't start!

Have you checked ALL the marks line up?

[Krtek]

What exactly do you mean by ALL the marks? There are two on the camshaft sprocket, which others should I look at?

[StumpyFingers]

IU think on TDC the two marks on the camshaft which are opposite each other should line up exactly with the head. ( i.e level )

[Krtek]

Okay, so ALL of those two marks should be level with the head itself (while the engine is in TDC). I think I get it

[stretchy]

Yup that's right; so you turn the engine over by hand by putting long socket in lhs of engine and with the other cover (above flywheel) removed you can see the marks on the flywheel; there should be T, F and II. T is the one you want. You have TDC and this is when the spark will fire.

Taking the top cover off the engine to expose the cam, the sprocket it's bolted to has two marks 180 degs opposite each other. OUT should be level with the head on the FRONT (exhaust side) with the other mark (line) level with the inlet side, it can be 180 degs out so just turn the flywheel again. The wedge to the LHS of the chain should be down a little at least, bit hard to explain but pics on my E-Bay ad.
As long as the marks line up the chain is OK, if not it's stretched.

Mine now starts a treat, mind you it's not a touch on my TTR-250 so it's on E-Bay for sale.

Item number: 260416250915
Doing up another XL200R, so little time, so many bikes!